In standard Public Switched Telephone Network (PSTN) systems, it is well know to manage incoming calls using a Private Automated Branch Exchange (PABX) to transfer calls to the intended recipient. FIG. 1 is a simplified schematic diagram of a prior art Enterprise context where an enterprise 11 has a PABX 12 which routes incoming calls 1 to telephones 13a, 13b etc. Details of the operation of the PABX are not discussed in detail as they are considered within the knowledge of one skilled in the art.
When an incoming call 1 is received from the PSTN network 10, the PABX 12 diverts 2 the call to the required extension. If the phone 13 at the extension is unanswered, the PABX 12 switches the call to the voicemail system 14 whereby the caller is invited to leave a voicemail for the intended recipient. In most enterprises the telephones are standard analog or digital devices.
In enterprises employing an intranet, voice-over-IP (VoIP) phones may be used with enhanced flexibility. This situation is shown in FIG. 2 where a call 1 is received by way of a standard PSTN network 20. However, in this case, communications within the enterprise 24 are effected by specific VoIP phones 22a, 22b etc. The VoIP gateway 21 receives the incoming call 1 and depending on the intended recipient, transfers 2 the call via the intranet 25 to the required VoIP phone 22. Communication over the intranet 25 is via TCP/IP data transmission as is know in the art. If the incoming call is unanswered, the call is diverted to the voicemail system 23 and a suitable notification sent to the recipient's VoIP phone.
While such VoIP systems present significant improvements in flexibility, dedicated VoIP phones are more expensive than standard PABX devices, such as analog or digital telephones. It would therefore be desirable to provide a system which not only provides for efficient call and voicemail handling analogous to the VoIP approach, but one which is backwards compatible with legacy telephone systems. It would also be desirable to provide a telecommunications system which is adaptable to systems having existing disparities between the technical level of an enterprise Information Technology (IT) infrastructure and its telephone system. For example, such a disparity may occur where an enterprise has an intranet, and retains a legacy PABX-based telephone system. It is a further object of the invention to provide additional functionality which leverages the functions of VoIP systems when coupled with an intranet and standard PABX-based systems, particularly in the context of voicemail handling.